As posed, this question has no answer and it might not be able to get work-shopped into an answerable form. Critically, though, I do not think that this makes it off-topic. I think that is often, and definitely in this case, a category error. Knowing the reasons that a question cannot be answered can be useful both for the asker and the community as a whole. But, I stress, there must be strong and well-articulated reasons for "there is no answer" to be a good answer. "I can't think of an answer," doesn't cut it.
(In this case, the reason is that terrain maps are widely understood to have fractal properties, meaning that it is nearly impossible to say if those features are small islands, big islands, or continent-scale land masses just by inspection.)
In order to be answered, what has to happen is that the asker's underlying (and probably at the time unconscious) assumptions about the map need to be teased out. (Probably in chat.) The existing answer takes one tack-- the underlying assumption about travel times.
Another tack is run with the idea that the planet is earth-sized, and then confirm that the map is the maps of the whole planet. And then try not to think too hard about map projections, because clearly if the asker had been thinking about map projection styles they would have had a characteristic scale in mind.
A third (related) tack would be to ask questions about, say, cold zones in the north or south (i.e., are there polar effects that would break the fractal assumption at high ends.)
Without such information, the answer is, "There is no answer, here's why." With such information, the question might have a more direct answer or estimate.